The work temperature of ICs is limited. When the temperature rises to exceed the allowed threshold, the circuit is operated probably in error or burnt out, resulting in a need of temperature detector circuit for necessary protection, especially to expensive devices such as CPU. For example, temperature switches are used to detect the temperature of IC to determine if it exceeds the allowed range, so as to immediately turn off power supply or start up remedial program to avoid the IC to be burnt out or operated in error.
FIG. 1 is a diagram of a conventional temperature detector circuit. The temperature detector circuit 10 connected between supply voltage VDD and ground GND will generate a signal on its output 17 when the temperature reaches a predetermined target temperature. The circuit 10 comprises a proportional-to-absolute-temperature (PTAT) current source 12 connected between the supply voltage VDD and a node 13, a resistor 16 connected between the node 13 and ground GND, a transistor 14 whose base connected to the node 13, whose emitter connected to ground GND and whose collector connected to the output 17, and a current source 18 connected between the supply voltage VDD and the output 17. When the temperature rises, the current I(T) provided by the PTAT current source 12 also increases and, as a result, the voltage on the node 13 rises. Eventually, the voltage on the node 13 will be so large to turn on the transistor 14 and thereby generating a signal on the output 17. Scheming the parameters of the circuit 10 will output the desired signal when the target temperature is reached, for example by the temperature detector circuit disclosed in U.S. Pat. No. 5,039,878 issued to Armstrong et al.
However, the parameters of IC devices are generally temperature dependent. If the parameters of elements in an IC shift from the design due to process variations, the circuit 10 will generate the trigger signal in advance or in delay, instead of at the target temperature. Unfortunately, process variation for ICs is unavoidable and the operation of the above-mentioned circuit 10 is dependent on precise process parameters. In mass production, due to the process variations, the distribution curve of the products for the actual trigger temperature becomes wider, and uniform and precise performance cannot be obtained. Moreover, since all elementary parameters of the circuit 10 are temperature dependent, once process variations presented, the actual performance at high temperature is difficult to be predicted at room temperature. In other words, it's hard to realize the circuit 10 in an IC with precise behavior at predetermined temperatures. Further, the trigger of the circuit 10 needs to overcome the turn-on voltage (Vbe) of the base-emitter of the transistor 14, which mechanism results in longer response time.
Therefore, it is desired a new temperature detector circuit and method thereof.